An organic thin-film solar cell is a solar cell using an organic thin-film semiconductor such as a mixture of a conductive polymer and fullerene. Compared to solar cells using inorganic materials such as silicon, copper indium gallium diselenide (CIGS), and CdTe, the organic thin-film solar cell has the advantage that it can be produced by a simple method at a low cost. On the other hand, the organic thin-film solar cell has the problem that it is inferior in power conversion efficiency and life to the conventional inorganic solar cells. This is because factors that are difficult to control, e.g., the purity, molecular weight distribution, and orientation of a semiconductor material have influence on the characteristics of an organic semiconductor used in the organic thin-film solar cell.
Under the circumstances, various improvements have been made to increase the power conversion efficiency of the organic thin-film solar cell.